Notably, inactivation of CXCL1/KC by SpyCEP extended beyond the site of infection, affecting serum CXCL1/KC levels in mice infected with wild-type S. pyogenes (median, 57 ng ml−1; range, 43–84 ng ml−1) compared with those infected with the cepA mutant (median, 75 ng ml−1; range, 48–99 ng ml−1; P < 0.05) (Fig. 3). This evidence concerns the gene CXCL1 and infection.